[popOver] Should add maxHeight if popOver won't fit at all

[IanCStewart]

popOver's that won't fit on top or bottom get aligned in the middle now. If a popOver is bigger than the window height you're missing both top and bottom of the popOver.

this seems weird...

[IanCStewart]

Partial fix in branch issue-#745. Seems to work initially until u resize to a bigger screen. This happens because the ref.height uses the old height and not the rendered height.